Generally, thermoplastic resins have lower specific gravity than glasses and metals and can have good physical properties such as moldability and impact resistance. Recently, plastic products have rapidly replaced conventional glass or metal products, for example, as components for electrical and electronic goods, as these goods have increased in size, to provide more economical and light weight products. Accordingly, the appearance and function of the plastic products have also become increasingly important when they are used in housings of electrical and electronic goods. For example, there is a need for plastic materials which can provide scratch resistance, impact resistance, and flame retardancy.
Polycarbonate (PC) resins, in particular, blends of polycarbonate and a vinyl copolymer (such as a blend of PC and acrylonitrile-butadiene-styrene, or “ABS,” copolymer) can have improved processability while maintaining high notch impact strength. Accordingly, such blends have been widely used in the production of heat-emitting large-size injection molded products such as automobile parts, computer housings, office equipment, and the like. Further, polycarbonate resins can obtain good flame retardancy even with a non-halogen flame retardant, which can be environmentally advantageous. However, polycarbonate resins have a drawback of poor scratch resistance.
In contrast, acrylate resins, such as polymethylmethacrylate resin, can have good transparency, weatherability, mechanical strength, surface gloss, adhesive strength, and excellent scratch resistance. Polymethylmethacrylate resins, however, may not have adequate impact resistance and flame retardancy for various applications.
Conventionally, a hard coating method has been used to improve the scratch resistance of plastic products. The hard coating method can include the steps of coating a surface of an injection-molded resin with an organic-inorganic hybrid material and curing the organic-inorganic hybrid material on the surface of the resin using heat or ultra violet light. However, the hard coating method requires an additional coating step, which can increase processing times and manufacturing costs and it may cause environmental problems. With recent increased interest in environmental protection and reduction of manufacturing costs, there is a need for a non-coated resin which has scratch resistance without using the hard coating method. Also, it is important to develop a resin with good scratch resistance for the housing manufacturing industry.
One attempt to improve both scratch resistance and flame retardancy alloys polycarbonate, a vinyl copolymer (such as ABS) and acrylic resin, such as polymethylmethacrylate (PMMA) to prepare a PC/ABS/PMMA resin. However, it can be difficult to obtain high transparency and colorability due to low compatibility of the resins and the differences between the refractive indices of the polycarbonate resin and ABS and acrylic resin. It can also be very difficult to use an alloy of PC and PMMA in housings of electrical and electronic products. Due to the different refractive indices of the PC resin and the PMMA resin (1.59 and 1.49, respectively), the alloy of PC resin and PMMA resin may scatter light. This can makes it difficult to provide color with high chroma, and a melt joining line is clearly shown during extrusion.
Korean Patent Publication Laid-open No. 2004-0079118 discloses a method of lowering the molecular weight of polycarbonate during a kneading process using metal stearic acid ester in order to improve the compatibility between a polycarbonate resin and a (meth)acrylate resin. However, the blend of the polycarbonate and the methacrylate resin can have significantly reduced mechanical properties.